Improving loss testing efficiencies through enhanced OLTS abilities

July 15th, 2016, Published in Articles: EE Publishers

 

An optical loss test set (OLTS) is a well-known device for its advantages in speed and accuracy over the more conventional light source and power meter. This makes the OLTS a great fit for applications with high fibre counts such as fibre to the home (FTTH) passive optical networks (PONs), structured cabling and data centre installs.

Fig. 1: Inaccurate references due to damaged or dirty connectors. Fig. 1a: Bad connectors.

Fig. 1: Inaccurate references due to damaged or dirty connectors.
Fig. 1a: Bad connectors.

Let’s look at changes to the OLTS technology in regard to meeting the requirements of the ITU-T G.650.3 standard.

Fig. 2: Accurate references using good connectors. Fig. 2a: Good connectors.

Fig. 2: Accurate references using good connectors.
Fig. 2a: Good connectors.

Referencing: A key step in testing

Inspection – the first step

Accurate test results start with accurate references, which can only be achieved using test cords that are in good condition. Fibre inspection is the essential first step in ensuring that accurate references and measurements can be made. Fibre inspection was introduced as an OLTS feature in 2002 and at that time it was performed manually, with connector health being assessed visually by the technician. The quality of the assessment depended on the “eye”, knowledge and discipline of the technician and thus varied immensely.

One improvement brought forth is the integration of EXFO’s fully automated line of fibre inspection probes, allowing for thorough assessment and certifying connector health in a mere matter of seconds. These rely on sophisticated algorithms that automatically centre, focus, capture and analyse the connector image without any intervention required. This means achieving repeatable and accurate inspection results as per the IEC-61300-3-35 or internal standard, 100 % of the time.

Accurate references are crucial in getting accurate results, but what are the correct test parameters and expected results in a good reference? This question may easily be answered by an expert but is not so evident for someone whose job involves using multiple instruments in complex testing environments, with often minimal training. Previous OLTS test sets could measure reference values but did not have a diagnostic tool to assess these values, This tool bridges the gap and goes beyond the call by guiding the user through an animated step-by-step reference process on a user-friendly interface. This reference wizard automatically assesses test cord losses according to pre-programme certifier – which automatically assesses test cord losses according to pre-programmed pass/fail thresholds. This means that now any user will know if the reference values are accurate or not, thanks to a simple interface and a powerful, automated diagnostic tool.

Fig. 3: The MAX-940 test cord verification method.

Fig. 3: The MAX-940 test cord verification method.

ORL reference and calibration

Optical return loss (ORL) is an all too often overlooked but vital measurement which is directly linked to connector cleanliness. Another aspect of the referencing process that was confusing to users was the ORL reference and zero calibrations. The main difficulty using previous OLTS test sets in the industry arose from the fact that a mandrel tool had to be used. Users would often not know how or when to do a mandrel wrap. The tool removes this difficulty as it does not require performing a mandrel wrap. Non-reflective terminations are integrated in the instrument’s optics for self-calibration during the reference process. No more mandrel wrapping means saving time while ensuring accurate references in just a few seconds by following the animated, step-by-step FasTesT process.

Fig. 4: Reference modes.

Fig. 4: Reference modes.

Test cord verification

The OLTS also comes with increased accuracy thanks to a new feature called test cord verification allowing assessment of the connector loss of reference test cords. Measuring mated connector loss is not only a crucial element in assessing reference test cords but also ensures accurate loss measurements which is very important when measuring low-loss short fibres.

This test cord verification method allows compliance with the industry’s well-known one-cord reference method. EXFO’s reference method cuts testing time in half whenever bidirectional measurements and the one-cord reference is required. It allows measuring single mode fibre loss and bidirectional ORL without disconnecting fibres, under five seconds at two wavelengths – all that at the touch of a single button.

Test speed

Testing speed is also a key factor when selecting an OLTS. The automation of the measurement through the FasTesT feature greatly minimises user manipulations and errors. The FasTesT technology is said to be the fastest OLTS in the industry. Automated, bidirectional insertion loss and fibre length test is performed in five seconds at three wavelengths.

Fig. 5: Continuity feature.

Fig. 5: Continuity feature.

Communication between users

Communication between users is also essential; knowing whether or not your colleague is ready to test at the other end avoids wasting time. Usually the technicians at each testing end have to communicate their testing phase. But what if the test sets at each end could “do the talking” for the technicians? This is exactly what the new real-time continuity feature is about in the tool. The main and remote units will both emit visual and audible signals to let the technicians on both ends know that a connection has been established on the specific fibre under test. This allows the technicians to start the test right away, saving time on each fibre tested. When testing high fibre count cables this can represent hours of testing time saved, or weeks over an entire project. This simple feature saves an immense amount of time for simple fibre identification in large patch panels to find a specific mislabeled port, as compared to the typical light source and power meter method. On top of the continuity feature, the MAX-940/945 also comes with text messaging capabilities. This feature allows users to send text messages through the fibre under test.

Fig. 6: Text messaging on the MAX-940.

Fig. 6: Text messaging on the MAX-940.

Retesting failing fibres

Failing fibres are usually due to connector cleanliness at the end of the test cords or optical distribution frame (ODF) interface. Bad splices, macrobends or other factors are usually detected beforehand with an iOLM/OTDR test. In all cases, re-testing is required after any corrective action. Retesting a fibre involves a series of time-consuming, relatively complex steps. These steps include: going back into the test results; identifying and selecting the fibre to re-test through record-keeping (paperwork); delete the bad fibre result to avoid duplication; go back in test mode; adjust fibre-naming structure, including the cable and fibre name for the fibre to retest; retest the fibre and save the result, and repeat steps 1 to 6 for other failed fibres.

Fig. 7: Results tab clearly showing the pass or fail status

Fig. 7: Results tab clearly showing the pass or fail status

Connectivity

Once the job is done with the test results stored and validated, the user needs to perform one or more of these tasks:

  • Exporting the raw data file to a computer or to the cloud.
  • Creating a report.
  • Sending files and/or reports.

PDF reports can now be directly generated and transferred, using a standard USB memory stick, the RJ45 network port or wirelessly.

Loading the raw data file into EXFO’s FastReporter 2 software opens the way for a host of new reporting capabilities, namely customer-specific templates, custom logos and fibre characterisation with the possibility of consolidating iOLM/OTDR and connector inspection results into a single report.

Case study

A customer recently tested the  MAX-940 for an installation job of a data centre interconnect cable containing 864 fibres. A job like this typically takes around six hours. With this fibre certifier the testing time has been brought down to  2,5 hours, i.e., 65% of time savings and three times more productive. Remember two technicians are involved for this specific six-hour job; the customer saved almost eight man-hours. At this pace, including the costs of having two technicians in the field, it is only a matter of weeks before the investment in this OLTS is recouped.

In this specific project, the customer said that the continuity feature, the test again function and the faster testing speed were three key aspects in saving time.

Contact Chris Nel, Lambda Test Equipment, Tel 012 349-1341, chris@lambdatest.co.za

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